We are further examining the behavioral effects produced by drugs or lesions that damage the monoamine systems of brain and the manner in which the behavioral effects of such brain damage can be reversed by appropriate drug treatment. In particular, we are attempting to determine whether the monoamines (serotonin, dopamine, and norepinephrine) produce their behavioral effects by alterations in stimulus input, associative processes and/or alterations in response systems. Such an assessment will be made by examining alterations in acquisition of a classically conditioned nictitating membrane response in the rabbit following selective destruction of the monoamine systems of brain, and an attempt to reverse these functional effects of brain damage through treatment with monoamine precursors (L-5-HTP and L-DOPA) and neuroleptic and antidepressant drugs such as chlorpromazine and imipramine. The mechanisms for such reversal of brain damage will be examined electrophysiologically and neurochemically in slices maintained in vitro which incorporate the pre- and post-synaptic elements of the monoamine systems. Finally, we are continuing our investigations on the neurotoxic effects of various halogenated arylalkylamines.